A case of mis-identification

by Mike Samworth

After looking at a sample taken from the pond in the grounds
of where I work, I was puzzled by some green algae. There seemed
lots of this particular species in the sample and so I set about
trying to identify it. Rather small in size and somewhat
club-shaped it wasn't familiar at all.

Flicking through various books in a quite unsystematic way I
had narrowed it down to two, Characiopsis sp. or Characium
sp.

Characiopsis
(left) and Characium
(right).

I wasn't particularly confident with either genus but since it
turned out that the former has no starch formed, an Iodine
solution test should do the trick. So I made a note to get some
from work. By the time I had, a second look at the sample
revealed some further development. The cells were no longer
singular and were in fact two or three cells long; this was a
filamentous alga! Further features noted, such as concentric
rings around one or two of the cells made me realise this was in
fact Oedogonium.

There are over two hundred species in this genus. It is a
filamentous type where the cells divide by a characteristic
method. It is this division that causes the rib-like bands at the
end of the cell. The number of "ribs" present indicates
the number of times the cell has divided. Oedogonium
produces motile spores and these eventually settle down and
germinate to form new plants. It is this stage that I had come
across, the so called germlings. They looked peculiar at one end
because they have a star-shaped disc or holdfast.

Oedogonium
germling with holdfast, and first division.

This just goes to show how easily we fall into too speedy an
identification. Also how important it is to make observations
over a period of time before coming to any hard and fast
conclusions. Above all it is but a learning experience and a
great deal of fun, and that is what really matters. Oh, this is
how it normally looks!